Source Code for Flex 3

You might want to check out Flex opensource

If you have the FlexBuilder already installed, you would be pleasantly surprised to discover it on your hard disk

All the action script files for flex controls can be found at

• <FlexBuilder installation directory\ Flex Builder 3\sdks\3.1.0\frameworks\projects\framework\src\mx\controls>
• <FlexBuilder installation directory\Flex Builder 3\sdks\3.1.0\fbpro\projects\datavisualization\src\mx\controls>

If you want to start using and customizing the flex controls, the source code of the base controls is your saviour.

In my opinion, reference to the source code of the base controls must be the first step for anybody trying to customize the base controls. It was really surprising that I have not come across any documentation or pointers for locating the source code of the flex controls or probably I havent spent enough time in exploring what packages along with the flex sdk.